Fluidized iron ore reduction process and apparatus



Dec. 8, 1964 T. F. oLT ETAL FLUIDIZED IRON ORE REDUCTION PROCESS AND APPARATUS Filed June 29. 1960 United States Patent O M 3,150,498 FLUHDEZED IRON @RE REDUCTION PROCESS AND APPARATUS Theodore F. Olt, William E. Marshall, and Samuel A.

Beil, Middletown, Ohio, assignors to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio Fied .lune 29, 1960, SenNo. 39,691 7 Claims. (Cl. 75-26) The blast furnace is still the most economical means for smelting iron in locations where coking coal and good quality iron ore in lump form are available without excessive transportation costs. Not all locations have these advantages; andV additional problems are presented by the growing cost of lump iron ore, and the increasing availability of ore substances which, while high in iron (before or after beneciation), are nevertheless in a iinely divided form unsuitable for use in the blast furnace. Much work has been done in an endeavor to convert such ores or ore derivatives into coherent masses of a size which will not be carried out of the furnace with the blast.

There are locations where a supply of coking coal is not available, but where a gaseous fuel such as natural gas is plentiful and cheap, and where ores may be obtained (especially where finely divided) at moderate'cost. These vconsiderations have led to substantial research into ways of reducing iron ores in fluidized-solids reactors by means of reducing gases. Various procedures have been developed, including ones Vin which the processing gases are recirculated and treated in a closed recirculatory system, and including those in which the processing gases are essentially sent through the reactor a single time only.

Processes of the first type generally require a very large capital outlay, especially since it is necessary to treat the gases both inside and outside the recirculatory system. Processes of the second type have also generally required a large capitaloutlay, and they have the further disadvantage of producing large quantities of tail gases which must be used or disposed of elsewhere.

It is a basic object of this invention to provide a procedure of the second type which is higher in efficiency and therefore lower in cost than other procedures of the type for various reasons but especially because all of the combustible values of the gases employed in it are utilized in the process itself.

It is also a basic object of the invention to provide an apparatus for the purpose described which will involve less capital outlay per unit of iron produced than has been possible hitherto. Y

These and other objects of the invention, which will be set forth hereinafter or which will be apparentV to the skilled worker in the art-upon reading these specications, are accomplished by that procedure and in the use of that apparatus of which an exemplary embodiment will now be described. The drawing is a diagrammatic representation of the apparatus assembly. The entire description which follows is intended to be taken as an example of the practice of the invention in the best form known to the inventors.

The process involves the use of gaseous fuel under pressure. The fuel will normally be natural gas consisting essentially of methane, although if available other hydrocarbon gases may be employed such asv ethane, butane, propane, and mixtures. Y

It is desirable to maintain in the reactor a'pressureA ofsubstantially 25 to 100 p.s.i.a. Natural gas is obtainable under these pressures; but the pressure of any available gas can be increased by the use' of. a pump. With some natural gases it isv desirable to pass them first 3,160,498 Patented Dec. 8, 1964 ICC through a desulfurizer indicated in the drawing at 1. The desulfurizer may be of any of the types known in the art such as, but without limitation, a desulfurizer employing oxide of iron.

The pressurized gas is next sent through a steammethane reformer 2, employing a catalyst as well known in the art. Fuel entering at 3 is burned to heat the gases I in the reformerand to provide the required endothermic heat of reaction. Coils of tubing 4 in the upper part of the reformer constitutea boiler. When water is introduced into the coils, steam is generated, some of which is sent to the reformer with the natural gas through a conduit 5. Excess steam can be drawn off `at 6 and used for heating or the production of power.

In the steam-methane reformer, the natural gas is f converted into gases having a high reducing potential as respects iron oxide yat the proper temperature providing the moisture content is llow enough. The mostr effective way of drying the gasesl is by-means of a gas cooler 7 in whichthe gases are cooled by means of water to a temperature of about F. with consequent condensation of moisture. A typical but non-limting gas composition after cooling consists of 6.9% CO2, 15.1% i

CO, 70.9% H2, 0.8% H2O, 6.2%V CH4, and 0.1% N2.

lt is necessary to reheat the processing gas to a temperature 'of about 1600 F. before it is sent tothe reactor. For this purpose there is shown in the drawing a preheating furnace 8 utilizing fuel entering at 9. Thegases are carried to a reactor 10' through conduit means' 11.

The finely divided iron ore which is .usually received in a damp or wet condition is passed first through a drying kiln 12 and then over a screen 13. Any ore materials which cannot pass the screen aresent through a mill 14 for crushing, and are delivered to a second screen 15. Any suitable mill 'may be employed for crushing, including'rod mills, ball mills, swing-hammer mills and the like. There is a return 16 for over-sized materials from the second screen 15 to the entrance side of the mill. Only those ore materials which are capablel of passing the screens are delivered by a conduit 17 to an ore preheater 18. The Vmesh sizes of the screens may be chosen bythe skilled worker in the light of the uidization conditions to be encountered. Twenty mesh screens may usually be used; but largeiior smaller mesh sizes may be chosen.

tinuous agitation, or to iuidization, the materialsuare heated to a temperatureofl about ll00-1300 F;r byl Air is shown the direct combustion of a fuel with air. entering atl `19 and fuel A-at 20. The preheated oreis dedelivered by a suitable conduit or conduits 21 to theV upper part' of the reactor 10. The delivery means includes one or more lock hoppers 22, the purpose of which is to pressurize the-*heated ore `sov as to convey` it into the reactor. Any suitable gas. stripper l22a may -be inserted between the ore preheaterk and lock hoppers to prevent the reactor atmosphere from becoming contaminated with the atmosphere in theore preheater. f

The atmosphere in the reactor is strongly reducing, whereas the atmosphere in the Vore preheater is usually oxidizing, inasmuch as complete combusitionofthe fuel In the ore preheater, 'in which the nely divided ore substances are subjected tol con-l Thetreated gases, as has'been indicated, enter the' reactor 10 at a temperature usually between 1400 and` 1700 d?. A single multi-bed reactor has ,been` indicated Ain the drawing. There may be morefthanone ofi such reactors, or single-bed reactors connected in parallel or in series may be employed. `In some instances fluidizing devices operating on the principle of cyclone separators may be used. The essential thing is that the reducing gases at the proper temperature shall come intimately into Contact with all portions 'of the ore substances in the reactors or reactor system so that efcient'lreduction can take place. Y Y

The tail gases from the reactor are carried by a conduit 23 to a cooler 24 which again maybe lav cooler employing water. The cooled gases will be employed to cool the ore from the reactor 19. The reduced ore substances .are shown as carried by a conduit 25 to an ore cooler 26. The action of the gas cooler 24 will be not only to cool the tail4 gases to the point wherethey can be used to cool the ore to a temperature Vbelow the reoxidation'temperature, but

also to-remove from the .tail gases moisture picked up Y during the reduction. Thus the cooled gases, at a temperature of about 100 F., while not strongly` reducing will at least be neutral so as to vprotect the reduced 'materials from reoxidation. Y J

. The ore cooler 26 may be aV fluidizing apparatus of any of the kinds mentioned above, the object being to 'bring the hot reduced materials into intimate contact with the cool and essentially inert'washed gases. Theore will be adequately cooled'if intimatelyadrnixedv with a suffi' -Zdmay be considered as aY cycloneseparator or the like f acting to separate the reduced materialfrom-thegas stream.V v f The minimum temperature of reoxidation will vary with the kind of ore treated in the system; but iron reduced at l400 F. from a good grade ofmany finely divided ores will not reoxidizeif below about 500 F. when eX- posed to air. e Further cooling of the reduced ore may be'v magneticY separator is indicated at-28. |Ihe magnetic'separation may befrcarried on in air providing theoreduced materials are .below the reoxidation temperature.r Otherwise the magnetic'separator will be locatedin a protective atmosphere. The tailings from the reduced material are, ofcourse, taken out of the system at 29, andthe finely divided `reduced Vrnaterialrnay,be delivered by means 30 to aibriquetting press 61. lFor. mos-t uses the briquettes will be melted in a suitable furnace such as an electricare furnace (notshown). Frornl goodquality ores in the .Way described, it is readilygp'ossible to make .a product containing 94% iron` with a silica content of less than'l 3%'.V AFor reduced materialswhichdonot respondwellto magnetic separation, apparatus element'ti` ma'yibe omitted. f Y The cooledgases leave the ore cooler Vor separator at ,the point marked 32, whence they are delivered by-.conduits, not shown, tol a secondV gas cleaning system, .riot

shown, andv then to the various places. in Vthe system at" ,Y whichrfuelis required.V Thus the fuel introduced into the. steam-methane reformer 2 atthe point `3,`theffuel usedA in the preheatfurnace l8 at'9, the fuel-.used in the drying Yi, kiln I2 and the yfuel'introdu'ced into the -ore preheateri' .13 at 20 can allbe supplied fromthe tailgasesderivedfl' from the device 26 at 32;; y=Ithas'beeni'found-.that the fuel requirements of the systemv are-such as touse-.up .f all of the tail gasesr available'at'l. Since the combustionV i -of the fuel inl thei 'steam-methane.reformer, the gas preheat furnace, theadr-ying kiln and thelore preheater is corn-V plete in each instance,jthesys tem fully` employs inuseful 4 operations al1 of the combustible values of the tail gases, and does not'produce tai-l gases in excess which must be Vdisposed of or used elsewhere.

The thermodynamicpeificiency of the system is there- 5 fore very high, and is superior to that of systems heretofore devised. All of the-operations described are useful in the making Aof the reduced product in the manner taught herein; butthe system involves no substantial heat losses Yexcepting at the two Vcooling devices '7 Vand 24. The system is `designed to handle any iron ore materials in'finely divided form; but it does not constitute a departure from the spirit of the invention to mix certain substances With the ore being treated. Thus a flux such aS limestone vmay be used with .the yfinely divided iron ores. `At the ytemperatures involved little trouble is had with sticking lor sintering'of the reducedfmaterials in the reactor or elsewhere. The reduced products of some ores have a L v greater tendency toward .stickingand sintering; and while la flux is not usually of much help in this regard, finely l divided Vcarbon .or iron carbidemixed with the ore will Y prevent sticking and sintering. yIn the system `of this invention itis 1possible to form duel-y divided carbon or iron However', since carbon can be releasedby the combination oftwo moleeulesof carbon monoxide to form carbon plus a molecule of carbon dioxide, and since this reaction is in part controlled by temperature, it is possible to release :carbon within the reactor in a controlled fashion byvarying the temperature and by introducing additional quan- At-ities or carbonaceous gases.V A very small quantity of carbon is usually suflicient topreventv sticking and sintering and no instances have been found where the quantity of carbon necessary was greater than about 8% of the iron, from 6% to 7%or lessfbeing avusual maximum. If Vthe quantity `off-fuel gas lavalilablefatthe point32 is not sufficient vvfor the purposes set .forth above, it goes Y without sayingt-hat'it maybe supplementedv by the addiition of some other fuel-Without losing any of the advantages of the process. Y Y Y n Y Y y Modifications maybe made in Vthe invention without departing from the Vspirit of it. The invention rhaving been'desoribedriin certain exemplary embodiments, what K `is claimed asnew and desired to besccured by Letters Patent-isi*y f l.v A process for the; iiuidiZed-solids reduction olf yfinely Y Y dividediron ores,'the 'said processY comprising the following stepsa, Y (A) preheating finely divided ironorein a preheating Y zone thnough the burning of afuel with air to form Y products of combustion substantially' devoid of re- 5 ducing values,

f f Y (B) `transfenring'thepreheated finely divided iron ore toaredu'cing Zone andfluidizing it in a reducing ate mosplrere while preventing the commingling of said 4.productsof combustion and said'reducing atmos- -phereyf' s (C) VVtransferring. the Vsaid reducing atmosphere after i usein the said reducing'zone to a cooling zone', and

there cooling and removing moisture from it',V (D) transferring the reduced ore productief step v(B) `to a cooling yzone and here treating it with the cooled reducing atmosphere from step (C) so as ,to kcool it Y to a temperature below the airV oxidation tempera- '-ture, while preventing the commingling ofthe Vatmosirheres in steps (13)-, (C) and (D), and e (E) transferringat leastea port-ionjofthe atmosphere from step (D) to the said preheating ,zone and Y, burning it as the fuel instep (A), whereby to avoid VV*1f-fthe -repeated vpassagm off gases through' the said process. f t 4V i Y VThe vprocessclaimed in clainil including` thewfurther 75stPsofr f N l 1` (F) producing the reducing atmosphere for use in step (B) by the steam reformation of a gas whereby a gaseous mixture consisting principally of hydrogen and carbon monoxide is obtained,

(G) applying heat to said gas in admixture with steam during said reformation, by the combustion of a gaseous fuel,

(H) employing as said gaseous fuel y'a portion of the atmosphere derived from step (D),

(l) cooling the said reformed gaseous mixture to remove moisture therefrom,

(l) and thereafter reheating the said reformed gaseous mixture before transferring it to the said reducing zone for the performance of step (B).

3. The process claimed in claim 2, wherein vthe rsh-eating of said reformed gaseous mixture in step (l) is accomplished through the burning'of a gaseous fuel With air, the said gaseous fuel being derived in part at least from the atmosphere of step (D).

4. The process claimed in claim 3 including the further steps of:

(K) drying the finely divided ore prior to the preheating of step (A) by burning a gaseous fuel with air in a drying zone, and

(L) transferring at least a portion of the atmosphere from step (D) tothe said drying zone and burning it with air therein to produce the heat required ffor drying, so that combustible values in the atmosphere from step (D) are used up steps (A), (H), (l) and (K) in the formation of products of combustion substantially devoid of reducing values, whereby all combustible values in any gases produced in the process will be consumed therein.

5. In yapparatus for the reduction of finely divided iron ore in la fluidized-solids reactor, by means of reducing gases passing through the reactor a single time only, the combination of a fuel fired ore preheater, a fluidizing reactor, means for delivering heated ore from the ore preheater to 4the reactor through a means for preventing commingling of the atmospheres of the reactor and the preheater, a gas cooler, means for delivering tail gases from the reactor to the gas cooler, an ore cooler, means for delivering reduced ore from the reactor to the ore cooler, means for delivering cooled tail gases from the gas cooler to the ore cooler wherein said cooled gases are oommingled with the reduced ore whereby to cool it to a temperature below the reoxidation temperature, and means for delivering gases from the ore cooler to the ore preheater for combustion with air in the preheater.

6. Apparatus as claimed in claim 5 including means for delivering lto said reactor reducing gases at a high temperature, said means comprising in the order named a steam methane reformer for converting gaseous fuel into a gaseous mixture containing relatively large quantities of carbon monoxide and hydrogen, a gas cooler for removing moisture from said gaseous mixture, and a preheating furnace for said gaseous mixture.

7. Apparatus as claimed in claim 6 including means for delivering gases from said ore cooler to said steam-methane reformer and said gas preheating furnace.

References Cited in the file of this patent UNITED STATES PATENTS 2,742,353 Ogorzaly Apr. 17, 1956 2,821,471 'Sellers Jan. 28, 1958 2,909,424 Iukkola Oct. 20, 1959 2,953,450 Viles Sept. 20, 1960 2,990,269 Hyde June 27, 1961 3,020,149 Old et al Feb. 6, 1962 3,021,208 Feinman Feb. 13, 1962 OTHER REFERENCES Iron and Steel Engineer, January 1958, pages 69 to 78.

Published by the Association of Iron and Steel Engineer Pittsburgh, Pa. Y 

1. A PROCESS FOR THE FLUIDIZED-SOLIDS REDUCTION OF FINELY DIVIDED IRON ORES, THE SAID PROCESS COMPRISING THE FOLLOWING STEPS: (A) PREHEATING FINELY DIVIDED IRON ORE IN A PRREHEATING ZONE THROUGH THE BURNING OF A FUEL WITH AIR TO FORM PRODUCTS OF COMBUSTION SUBSTANTIALY DEVOID OF REDUCING VALUES, (B) TRANSFERRING THE PREHEATED FINELY DIVIDED IRON ORE TO A REDUCING ZONE AND FLLUIDIZING IT IN A REDUCING ATMOSPHERE WHILE PREVENTING THE COMMINGLING OF SAID PRODUCTS OF COMBUSTION AND SAID REDUCING ATMOSPHERE, (C) TRANSFERRING THE SAID REDUCING ATMOSPHERE AFTER USE IN THE SAID REDUCING ZONE TO A COOLING ZONE, AND THERE COOLING AND REMOVING MOSITURE FROM IT, (D) TRANSFERRING THE REDUCED ORE PRODUCT OF STEP (B) TO A COOLING ZONE AND THERE TREATING IT WITH THE COOLED REDUCING ATMOSPHERE FROM STEP (C) SO AS TO COOL IT TO A TEMPERATURE BELOW THE AIR OXIDATION TEMPERATURE, WHILE PREVENTING THE COMMINGLING OF THE ATMOSPHERES IN STEPS (B), (C) AND (D), AND (E) TRANSFERRING AT LEAST A PORTION OF THE ATMOSPHERE FROM STEP (D) TO THE SAID PREHEATING ZONE AND BURNING IT AS THE FUEL IN STEP (A), WHEREBY TO AVOID THE REPEATED PASSAGE OF GASES THROUGH THE SAID PROCESS. 